a. Field of the Invention
The present invention pertains generally to the fusion of plastic pipe and specifically to the simultaneous fusion of multiple sections of plastic pipe.
b. Description of the Background
Polyethylene pipe is used commercially for the construction of pipelines for various applications such as natural gas, water, sewer, and other materials. In addition, polyethylene pipe may be used as conduit to protect transmission cables such as high voltage electricity, fiber optic telecommunication, telephone, cable television, and other signal cables.
Polyethylene pipe is typically joined through a process called fusion welding, the most common joint being a butt joint. A butt joint is formed by holding the two sections of pipe rigidly, performing a facing operation to square the ends of the pipes and prepare the pipes for welding, then heating the prepared faces of the pipes on a hot plate to the melting point, removing the heating element, and forcing the two melted faces together. The resulting joint may be cooled before being subjected to any handling forces. The result is a fused joint that is as strong or stronger than the parent material and is very reliable.
U.S. Pat. No. 4,990,209 issued to George Rakes entitled “Self Propelled Fusion Machine” (Rakes) is a machine adapted to perform butt joints on polyethylene pipe as described above. Rakes is incorporated herein by reference for all that it discloses and teaches. The Rakes machine performs the sequence of butt fusing in a semi automated fashion, with provisions for easily loading and unloading the pipe as it is welded. Additionally, the Rakes device performs the butt fusion process in an enclosed environment, adding to the consistency and throughput of the machine in all types of weather. After fusing a section of pipe, the Rakes machine advances and assembles another section.
The throughput of machines such as Rakes is limited to performing one weld at a time on a single pipe. In some applications, however, two or more pipelines may be run parallel to each other in the same ditch. In such applications, machines such as Rakes' machine must make multiple passes to assemble the necessary pipe for a particular installation.
Other machines are not as mobile as the Rakes machine. With machines that are not mobile, it may be common for the constructor to assemble a section of pipe to the pipeline, then drag the entire length of assembled pipe to advance the pipe for assembly. In such cases, the machine is fixed and the pipeline is advanced. The limiting factor in throughput is the fact that the welds can only be performed one at a time.
It would therefore be advantageous to provide a device and method of fusing more than one section of pipe at a time. It would be further advantageous if the equipment required for performing multiple welds were simple and easy to change over to different sized pipes.